1. Field of the Invention
The present invention relates to a sheet processing apparatus, a control method for controlling such a sheet processing apparatus, and a storage medium.
2. Description of the Related Art
Some of the sheet processing apparatuses, which have been known in the art, are provided with a plurality of stacking units designed like stacking trays in a stacker device that stacks sheets therein, where sheets are stacked on each of the stacking units.
Among these sheet processing apparatuses, there is one in which sheets of a small size (hereinafter, also referred to as small sheets) are stacked on each of plural stacking units in a stacker device and large sheets are stacked over the plural stacking units (see, for example, Japanese Patent Laid-Open No. 2008-87965).
However, when a small sheet is stacked on the first stacking unit or the second stacking unit included in the plural stacking units and a large sheet is stacked over both the first stacking unit and the second stacking unit, the following disadvantage may occur. That is, depending on the way of stacking sheets, the stacked sheets will become unstable.
For instance, when large sheets are stacked over plural stacking units where small sheets have been already stacked on one of plural stacking units but no sheet on the others, the staked large sheets may be leaned and become unstable.
In addition, even if small sheets are stacked on each of the plural stacking units, the stacked large sheets may be leaned and become unstable when a difference between the heights of the sheets on the respective stacking units occurs.